Adjustable steering columns are known in the prior art, in the case of which adjustable steering columns a casing unit of a steering column, in which the steering spindle of a steering shaft is mounted rotatably, can be locked releasably between the two side cheeks of a bracket part which is attached fixedly to the vehicle body. The locking takes place by the side cheeks being moved against one another by way of the actuation of a locking or clamping device, with the result that substantially non-positive clamping of the casing unit takes place. If the locking device is released, the position of the casing unit and therefore of the steering wheel which is attached at the rear end of the steering shaft can be adjusted relative to the position of the driver.
In known locking devices, the actuation for locking and releasing takes place by way of rotation of an actuating shaft via an actuating lever which is attached thereto. A locking device of this type is described, for example, in DE 10 2011 055 410 A1, in which a first cam carrier is arranged fixedly on a side cheek so as to rotate with it, and a second cam carrier with cams which are directed counter to the first cam carrier is attached on the actuating shaft. The cam carriers are lifted up from one another by way of a rotation of the actuating shaft out of an angular position, in which the cams of the one cam carrier engage between the cams of the other cam carrier, into a relative angular position, in which the cam tips bear against one another. Said lift can be utilized to press said side cheeks of the bracket part against one another by way of support against an axial abutment of the actuating shaft, which axial abutment is arranged on the bracket part. As an alternative, other mechanisms can also be used which permit a conversion of the rotational movement of the actuating shaft into translational bracing of the side arms, for example wedge plate/cam systems or gravity lock clamping systems, as known from DE 44 00 306 A1, or the like.
By virtue of the fact that the parts which can be moved against one another for bracing purposes, for example the cam carriers, have mechanical play in the known clamping systems, the actuating lever can vibrate and generate undesired rattling noise. Moreover, a restoring force acts on the actuating lever during the release of the clamping action, which restoring force can lead to likewise undesired snapping back of the actuating lever. In DE 10 2011 055 410 A1, both undesired effects are counteracted by the actuating shaft being connected to a damping device which damps a rotation of the actuating shaft about its rotational axis in at least one rotational direction. As a result, vibrations and noise are reduced, and the result is an equalized, braked movement of the actuating lever.
In order to realize the damping device, DE 10 2011 055 410 A1 proposes the use of a rotary or rotational damper with a rotor which, during a rotation about its rotor axis, has mechanical rotational energy removed from it, that is to say is braked or damped. To this end, the rotor is mounted in a housing such that it can be rotated about its rotor axis, which housing is filled with a highly viscous damping fluid which is displaced during a rotation of the rotor and in the process brakes the rotational movement of the rotor by way of internal friction and interface friction.
The defined and reliable function is advantageous in the case of the known rotational damper. The relatively complicated design is disadvantageous, however, in the case of which design the housing and the rotor shaft have to be sealed against the liquid fluid. Moreover, the use of liquids in the vehicle interior is fundamentally to be avoided as far as possible.
Thus a need exits for a locking device with an improved rotational damper which is less complicated to manufacture and has a high acceptance in automotive engineering.